Retarders are widely used in railroad marshalling yards to control the speed of the cars as they are being directed to their desired track and location. Controlling car speed is important. Cars should not exceed specific speed limits. Doing so can result in expensive and dangerous derailments. Some cars may need to travel significantly further through the yard than others, and some cars may be significantly heavier than others. Yet, heavier cars can pick up more speed and require more braking force to slow or stop.
Weight-responsive retarders such as the Type F4 skate retarder provide an amount of braking power proportional to the weight of the rail car. Skate retarders prevent cars from leaving the yard, which protects passing trains and surrounding property and persons. Each segment of the retarder includes a pair of levers joined together under the running rail and extending from opposed sides of the running rail. The levers hold a pair of braking rails, one on each side of the running rail. A hydraulic lift is activated to raise the gauge-side lever so that the braking rails are closer together than the width of a car wheel. A car entering the retarder will force the brake rails apart with a force proportional to the weight of the car. This braking force is applied to the sides of the wheels and causes the car to stop. Spreading the brake rails apart causes the levers to rotate about their knuckle joint, and raises the running rail and car against the force of gravity. The heavier the car, the more force needed to lift the car, and the more braking force applied to its wheels.
A problem with conventional F4 weight-responsive skate retarders is that they are not fail-safe. Power must be supplied to the hydraulic unit of the retarder to produce the braking force needed to stop a railroad car. The hydraulic lift moves the brake rails to their operating position. When power is cut off, the brake rails return to an open position that allows cars to pass through the retarder unimpeded. Weather conditions such as lightning strikes or mechanical malfunctions can cause a loss of power to the retarder and lead to dangerous situations in which the skate retarder cannot be used to stop a moving car. Derailments or crashes can occur that result in significant damage to cars, equipment and cargo, expensive clean up and yard downtime, and serious injury or loss of life to railroad personnel.
Another problem with conventional F4 skate retarders is their “power on” time. Power must be supplied to the hydraulic power unit throughout the day to keep the retarder operating. This increases power consumption and wear and tear on component parts such as in the hydraulic system. Leaks of hydraulic fluid are more prevalent, and more frequent maintenance checks and repairs are needed to ensure proper operation of the retarder.
A still further problem with conventional F4 skate retarders is that they are not universal. A right-handed retarder is needed when the braking levers need to be placed on the right-hand rail of the track, and a left-handed retarder is needed when the brake levers need to be on the left-hand rail. These limitations arise due to track spacing and electrical power locations. The railroad tie saddle has a wear plate on only one side. This plate must be located between the lever mechanism and the tie on its downhill side to maintain the proper alignment of the levers and protect the railroad tie from damage. Right-handed and left-handed retarders are not interchangeable, which results in increased inventory and ordering problems.
A still further problem with conventional F4 weight-responsive skate retarders is the disproportionate movement of the levers and their brake rails. Because the hydraulic cylinder is placed at the outer end of the gauge-side lever, when the hydraulic cylinder is deactivated or lowered, the gauge-side lever moves to its release position that allows the rail cars to pass through the retarder unobstructed. When the hydraulic cylinder is lowered, the braking rail mounted to the gauge-side lever moves a lateral distance of about one inch. Yet, the braking rail mounted to the field-side lever remains substantially stationary, which can result in the wheels of a car dragging on the field-side brake rail when in its release position. This causes excessive wear of the field-side brake rail. A great deal of attention and effort is needed to ensure proper alignment between the running rails and the field-side lever brake rail to ensure proper clearance when the retarder is in its lowered release position to minimize potential engagement with the car wheels.
A problem with conventional (non-F4) skate retarders is that they do not apply consistent weight-responsive braking force to the car wheels. Either too much braking power is applied to unloaded or lighter weight cars (causing the cars to derail), or too little braking power is applied to fully loaded or heavier weight cars (failing to slow or stop the car as desired). Both situations can result in loss of life and significant property damage. Skate retarders that are not weight responsive have difficulty applying a proper amount of force to a passing car. A non-weight responsive skate retarder with a low enough brake force to leave a light car on the track needs to be very long in order to stop a heavy, fast moving car. Longer skate retarders tend to be more expensive and reduce the storage capacity of the yard, which reduces the overall efficiency of the yard.
A further problem with non-weight-responsive (non-F4) skate retarders is the need for regular and frequent maintenance to ensure proper spacing and shimming of the brake rails. Because the brake force produced by the retarder is provided by springs, wear of the brake or rails results in a loss of braking power.
A still further problem with conventional skate retarders is maintenance difficulty. Ballast gravel surrounding the retarder prevents easy access to components such as the hydraulic cylinder, and could even jam the lever arms.
The present invention is intended to solve these and other problems.